Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to gas injection seal systems for centrifugal pumps and particularly to centrifugal pumps disk friction reducing injection rings and eye ring seals.
2. Description of the Prior Art
In the prior art, centrifugal pumps with closed impellers (i.e., those with shrouds on both sides of the vanes) have a cavity between the impeller and the pump casing. Also, a small radial gap exists at the eye of the impeller between the rotating impeller and the stationary casing, which is called the wear ring gap. The designs allow fluid at discharge pressure from the impeller to circulate behind the impeller shroud in the cavity between the shroud and the casing. It also allows a certain quantity of fluid to leak back to the suction side of the impeller through the wear ring gap. As the impeller rotates, the fluid behind the impeller creates a power loss due to the shearing of the fluid between the impeller shroud and the casing wall. The wear ring leakage also creates a power loss because the leaking fluid loses all of the energy that the impeller imparted to it and then is reintroduced to the suction stream to be pumped again.
The instant invention overcomes all of these problems. In the instant design, a set of seals is installed on the impeller that allows a low viscosity fluid (typically gas) to be injected into a chamber between the impeller shroud and the casing sidewall at a pressure higher than suction pressure.
On each impeller shroud there is a seal ring installed on the tip of the impeller""s outer perimeter. Another seal ring is mounted at the leading edge of the eye of the impeller. The seals installed on the tip of the impeller (tip seals) have a series of grooves formed in them that are open to the chamber on the backside of the impeller shroud. A gas is injected through a port in the case and into a chamber formed by the tip seal, the eye ring seal, the impeller shroud and the casing wall. The gas is then picked up by the grooves in the impeller tip seal ring inside diameter and is compressed by centrifugal force to a higher pressure than the discharge pressure of the impeller. It is then injected into the pumpage stream. The eye ring seals have pockets and inject gas at a low volume into the eye of the impeller. In this way, both leakage problems described above can be eliminated. The disk friction reducing injection mechanism drastically reduces the losses associated with disk friction and wear ring leakage losses. This combination increase pump efficiencies.
This invention can work on a variety of centrifugal pump types including double suction impellers; single suction closed impellers and open face impellers with a single shroud.